Valley residents woke up to find parts of Maricopa County cloaked in a thick fog on Saturday morning.

The National Weather Service reported fog in large swaths of the East Valley, including Mesa, Ahwatukee, Gilbert, Chandler, Apache Junction, Queen Creek and into Pinal County.

In Northern Arizona, the recent snow storms gave way to heavy fog early Saturday. Heavy fog was spotted on Interstate 40 east of Flagstaff and on Highway 260 near Show Low.

NWS officials warned there was practically zero visibility in the fog and instructed drivers to slow down or even delay travel.

Areas of fog continue to affect outlying areas surrounding Phoenix, into Pinal County (incl. Casa Grande). We are monitoring satellite imagery to see how widespread the fog is. Most areas of light blue represent fog or low clouds. #azwxpic.twitter.com/xFIsnG3BlJ